Grounded surface distribution apparatus

ABSTRACT

A grounded surface distribution apparatus and system is provided including elastomer encapsulated cable terminals, joints, taps, load-break switches, current limiting fuses and surge protectors, each enclosed completely within a metal sheath combined in various arrangements to perform operational functions required in loop and radial underground distribution systems. The cable terminals include a soft dielectric filler making a void-free interfacial engagement with the surface of a hard dielectric filler of a mating component. To provide for breaking a coupling under load, an arc-quenching follower is retractable into an axial cavity in the coupling components of the system and projectable therethrough upon breaking of the circuit and disconnecting of the components to provide an improved arc-quenching function. Thus, there is provided an underground system having security, operational safety and convenience.

The present application is a continuation of application Ser. No.660,748, filed Aug. 15, 1967, now abandoned.

The present invention relates to a new and improved grounded-surfacedistribution apparatus and system for underground installation such asrequired in loop and radial underground distribution systems. Moreparticularly, there is provided unique cable-terminal load-break switchelements which make possible hot-stick disconnecting, switching,sectionalizing and the like without moving the cable or the cableterminals and providing visible separation between grounded-surfacecircuit elements.

The present strong trend toward underground distribution of electricitybrings with it the need for new kinds of associated apparatus to providethe necessary system functions including switches, fuses, surgearrestors, cable terminals, taps and joints. The new aspect of suchapparatus is that it must be able to carry on its functions undergroundin contact with and at times under water. This means that every part ofthe circuit which is maintained at system potential must be surroundedby a continuous sheath of impervious, void-free insulation within acontinuous conductive grounded housing.

Commercial apparatus attempting to fulfill these difficult requirementsis still in the early stages of development. Prior known apparatus hasnot been entirely successful. In fact, the trend toward such undergrounddistribution systems is so new that standard nomenclature has not beenestablished by the electrical industry. The term "submersible" issometimes applied to these devices for want of a more appropriate term."Grounded-surface distribution apparatus" is a more appropriate and moretruly descriptive term for this class of equipment since a conductivegrounded-outside surface is a function requirement for operational andsafety reasons.

The essential and main ingredient in underground distribution ofelectricity is obviously cable which must carry distribution current andvoltage underground with trouble-free long life performance. Recentdevelopments in synthetic dielectric materials have made possible theproduction of solid polymer insulated cable with high performance andlow cost. However, the advantages of the new cable cannot be realizedfully without effective, safe and convenient means for connecting thecable to various devices required in underground distribution systems.By employing voltage grading and interfacial sealing techniques, it hasbeen possible to provide grounded-surface submersible devices to performfunctions of cable joining and terminating, load-break switching,sectionalizing, and fusing.

The term "grounded-surface" may be taken literally in that apparatus inthis category does in fact have a grounded external surface preferablyof metal thick enough to provide mechanical support and to carry faultcurrent if it occurs. Conductive plastic coatings will perform part ofthe function of grounding the surface but they may not provide safetyunder fault conditions.

Thus, it is an object of the present invention to provide a new andimproved grounded-surface distribution system.

A further object of the present invention is the provision of a new andimproved distribution system suitable for underground and submersibleinstallation.

A further object of the present invention is the provision of a new andimproved cable terminal for a grounded-surface distribution system.

A further object of the present invention is the provision of a new andimproved coupler for a distribution cable.

A further object of the present invention is the provision of a new andimproved load-break coupling suitable for grounded-surface distributionsystem application.

Yet a further object of the present invention is the provision of a newand improved arrangement of taps and connecting units for an undergrounddistribution system.

A further object of the present invention is a new and improved surgearrestor for a grounded-surface distribution system.

Another object of the present invention is the provision of a new andimproved fuse structure for a grounded-surface distribution system.

The difficult design problem in grounded-surface distribution apparatusis to put the entire high potential circuit inside the grounded housingsand still provide means for carrying out switching and sealing-offfunctions. In accordance with the present invention there is provided asystem which employs a combination of soft and hard dielectrics castinto place around the high voltage elements with compression springs atappropriate locations to maintain all critical interfaces void-free andunder pressure over all ambient variations expected in operation.

In accordance with one aspect of the invention each circuit ismaintained separately in its own grounded sheath with interfittingcomponents available to set up various functions such as load-breakdisconnect. In this case the two cable terminals are supported by arigid clamp mounted on a ground rod. The load-break features are presentin both cable terminals independent of each other. The switch blade is agrounded-surface inverted "U" coupling which may be removed with a hotstick from above. The operator moves only the coupling piece. The cablesand terminals are not moved or disturbed in the operation. The energizedcircuits are never exposed since loadbreak followers fill the connectoropenings when the switch is open. The open circuits are visiblyseparated and metallic grounds are between them. Insulated or groundedcaps can be secured or latched over the elements of the open switch, ifdesired. Thus, the switch whether open with separate caps or closed withthe "U" coupling, is completely safe and without hazard to operatingpersonnel working in close proximity to it.

In accordance with another aspect of the present invention, the morecomplicated arrangements carry the same features of system security,operating convenience and safety. For example, a three terminal tapswitch arrangement according to the present invention is very effectivein loop systems where sectionalizing is needed.

In accordance with the present invention a grounded-surfacecurrent-limiting fuse provides system security when used in the tapcircuits.

An improved surge arrestor provides convenient means for surgeprotection of the open position in loop circuits. Such a surge arrestoris also equipped for installation or removal with a hot stick.

The basic element of the present grounded-surface distribution apparatusis the cable terminal. It performs several important functions: (1)connection to the cable conductor, (2) grading of the field andprovision of a permanent seal over the cable insulation, (3) provisionof a disconnect and load-break element, (4) provision of a standardconical sealing surface to mate with various elements such as couplers,fuses, insulating and grounding covers, and (5) to provide interfittingof various elements having high versatility in meeting circuitrequirements by means of a rigid cylindrical housing of stainless steelwith locating means in precise bracket structures. All of theinterfitting elements employ the same standardized conical sealingsurface and latch spring geometry. The grounded cover of the cableterminal is latched into place providing the standardized conical sealwhich is waterproof due to the void-free interface held under permanentpressure by the latch springs.

In accordance with one aspect of the invention wherein a "U" coupler islatched in place between two cable terminals, the "U" coupler mayreadily be removed with a hot stick to provide load-break disconnecting.The "U" coupler and associated load-break terminals easily meet theusual requirement encountered with single phase distribution systems.The concentric neutral wires of the cable are connected directly to thecable terminal housing and serve to hold the cable in place by means ofsplit bolt connectors, then continue on to be connected together and toground. This firm connection is particularly important where systemfault currents are high.

The present devices are particularly well adapted for sub-surfaceswitching points or control centers. In such control center arrangementsthe loop can be separated and part of it temporarily grounded with agrounding cover and also it may be sealed off in the open position withan insulating cover or a surge arrestor. Versatile components thusprovide means for safely controlling, protecting and servicingunderground single phase loop or radial systems. Maximum safety isafforded to operating personnel by virtue of the continuous groundedsheath which covers all energized elements with rugged stainless steelwhich can carry the high fault currents which sometimes occur indistribution systems.

Another safety feature which is inherent in the grounded-surface systemis that open circuit positions always provide visible separation withsolidly grounded elements between the separate circuit terminals. Thus,when all circuit terminals are sealed and latched with couplers, fuses,arrestors, covers or the like as required, the sub-surface controlcenters provide the maximum in circuit reliability, the minimum incustomer outages, and maximum in safety and conveniences for servicing.

For a better understanding of the present invention, reference may behad to the accompanying drawings wherein:

FIG. 1 is an isometric view of a cable terminal with a grounding cap inplace according to the present invention;

FIG. 2 is a cross sectional view of the cable terminal of FIG. 1, andillustrating the electrical coupling components within the cableterminal;

FIG. 3 is a cross sectional view of the cable terminal of FIG. 1, takenalong line 3--3 of FIG. 2, and illustrating the plug-in connectorcomponents within the cable terminal;

FIG. 4 is a cross sectional view of the connector coupling components ofFIG. 3, illustrated to a larger scale;

FIG. 5 is an exploded view of the coupling components of FIGS. 3 and 4;

FIG. 6 is an isometric drawing illustrating a grounded-surfaceload-break switch employing two standard load-break cable terminals anda standard "U" coupler.

FIG. 7 is a cross sectional view of a "U" coupling unit taken along line7--7 of FIG. 6;

FIG. 8 is a cross sectional view of the "U" coupling unit of FIG. 7,taken along line 8--8 of FIG. 7, assuming that FIG. 7 illustrates theentire structure;

FIG. 9 is a top view of a single tap arrangement employing threeload-break cable terminals, and a tap manifold or bus in accordance withthe present invention;

FIG. 10 is an elevational view of the structure of FIG. 9 and furtherillustrating "U" couplers in phantom;

FIG. 11 is an elevational view of a three-point manifold or bus of thetype illustrated in FIGS. 9 and 10, illustrated in broken away section;

FIG. 12 is an elevational view of a surge protector for use with a cableterminal according to the present invention and illustrated partially inbroken away section;

FIG. 13 is a top view of the surge protector of FIG. 12;

FIG. 14 is a cross sectional view of a current limiting fuse for usewith terminals according to the present invention;

FIG. 15 is an alternate structure of a fuse connector for use withterminal taps according to the present invention and illustrating aremovable fuse arrangement;

FIG. 16 is an end view of the fuse structure of FIG. 15;

FIGS. 17 and 18 illustrate an alternate control center arrangementincluding a connecting unit having multilevel terminals to providedesired economy of space and apparatus;

FIGS. 19 and 20 illustrate the isolating or grounding of one of thelines in the control center of FIG. 17;

FIG. 21 illustrates in cross section a primary cable terminal for thegrounded surface submersible system according to the present invention;

FIG. 22 illustrates in broken away section a cable joint according tothe present invention;

FIG. 23 is an end or bottom view of the cable joint of FIG. 22 takenalong line 23--23 of FIG. 22;

FIG. 24 is a cross sectional view of the cable joint of FIG. 22, takenalong line 24--24 of FIG. 22;

FIGS. 25 and 26 illustrate a switching point assembly employing animproved "T" terminal; and

FIG. 27 illustrates a sub-surface switching point assembly.

Referring now to the drawings and particularly to the embodiment ofFIGS. 1, 2 and 3, there is shown the details of a cable terminal 30 witha grounding cover 32 latched in sealed position. The cable terminal 30includes a conducting housing 34 of suitable material such as stainlesssteel, and cylindrical in cross section. A cover 35 also of conductingmaterial such as stainless steel engages two side pins 36 in the housing34 in a spiral bayonnet action to compress an inner thrust spring 37 tobe compressed in the latched position as shown so as to exert an axialthrust on a soft elastomer dielectric filler 38 confined at its lowerend by a piston-like cup retainer 39.

The soft dielectric filler 38 is cast within the housing 34 to interfitwith a hard dielectric filler 40 which is firmly cast and locked intothe housing 34 but which projects from the end of the housing to providea standardized conical sealing surface 41 having a connector entrance42. Although the hard dielectric filler 40 is illustrated as formed oftwo parts 40a and 40b, it may be made of one piece if desired.

As used herein, the soft dielectric filler may be of any void-freedielectric soft enough to conform to the adjacent surfaces in void-freeinterfacial engagement under the loading of the selected thrust spring.It has been found that a soft poly-urethane or other limited crosslinked polymer, preferably castable, with a Shore A hardness of 20 to40, worked satisfactorily. As used herein, the hard dielectric fillermay be of any void-free dielectric hard enough to provide mechanicalstrength to position the components. Castable synthetic polymers such asepoxy resins having a Shore A of 100 or higher were found satisfactory.

The soft dielectric filler 38 is designed to receive a power cable 45 ofthe type having a basic insulation 46 and a sheath 47 as customizeddimensions. In addition to the sheath 47, the cable 45 may contain aplurality of strands of grounding wire 48. The end thrust spring 37permits a reasonable range in diameter variation and still maintains apermanent void-free interfacial seal between the insulation 46 and thesoft elastomer 38 even under submerged conditions.

The cable terminal 30 includes a connector 50 for terminating the end ofthe cable 45 and defining a cable connector 50a at one end. The cableconnector 50a has an elongated body of conducting material, such ascopper and the like, and defines a receptacle 51. A conducting pin orplug 52 is adapted for insertion into an elongated axially aligned pincavity 53 of the receptacle 51 to establish a low resistance connectioncapable of carrying rated current as well as momentary high currents.The pin 52 is connected to the short exposed end 45a, FIG. 2, of thecable 45, and the pin 52 is formed with an elongated axially alignedsocket 54 extending inwardly from the lower end of the connector. Afterthe central conductor 45a is inserted into the socket 54, a compressiontool or the like is used to compress the walls of the socket inwardlyinto tight engagement with conductor 45a and thus firmly secure andelectrically connect the pin 52 to the upper end of the cable 45. Thepin 52 includes a cylindrical pin portion 55 of reduced diameter adaptedto be inserted into the pin cavity 53 of the receptacle 51 to establishelectrical connection therewith.

The receptacle 51 around the pin cavity 53 thereof is square orparagonal in cross section, FIG. 3, and includes a plurality of planarouter faces 58 which angularly intersect one another, forming aplurality of longitudinally extending parallel upper ridges 59.Preferably, the ridges are provided with narrow, flattened upper faces59a, FIG. 4, which are tangent to a circle having its center on thelongitudinal center axis of the receptacle 51. Each planar face 59a ofthe receptacle 51 is bisected by a longitudinally extending slot 60extending upwardly from the lower end of the connector and terminatedadjacent the inner end of the pin cavity 53. The slots 60 bisect thefaces 59a into pairs of segments of approximately equal area, andthereby form a plurality of movable fingers 62, each including one ofthe ridges 59 and a pair of segments on its outer surface and a curvedsegmented, cylindrical interface forming a wall portion of the pincavity 53. The free ends of the fingers 62 are movable inwardly andoutwardly with respect to the longitudinal central axis of thereceptacle 51 and form the lower end portion thereof surrounding the pincavity 53.

In order to establish a relatively high contact pressure between thefingers 62 and the pin 52 and thereby further reduce the resistance ofthe connection and increase the current carrying capacity thereof, thefingers 62 are biased inwardly by a circular tension ring 63 which isslipped over the body of the receptacle 51 and bears against theflattened surfaces 59a on the ridges 59. Preferably, the ring 63 isformed of a thin band of high strength material, such asberyllium-copper alloy and is dimensioned so that the inner diameter ofthe ring is slightly less than the distance between the flattenedsurfaces on the ridges 59 on the diametrically opposite fingers.Accordingly, the ring 63 is under tension and is force fitted over thelower end of the body and moved upwardly thereon toward the blind end ofthe pin cavity 53.

The amount of inwardly biasing force exerted on the fingers 62 by thering 63 is selectively adjustable by movement of the ring 63 around thefingers of the receptacle 51. For example, the fingers 62 are moreeasily deflected near the outer or free ends, and when a ring of giveninternal diameter is positioned adjacent the free end, the fingers 62have less inward deflection of the free ends than when the ring 63 ismoved upward toward the blind end of the pin cavity 53. The flattenedsurfaces of the ridges 59 permit easier movement of the ring 63 thereonwithout gouging of the ridges.

From the foregoing, it should be noted that the cable connector 50aprovides a large contact surface between the connecting members thereofand additionally provides for an adjustable contact pressure over thelarge contact surface. It is not necessary to tighten any bolts orclamps for assembling the cable connector once the connecting membersare engaged since ample holding force is achieved by the contactpressure between the connecting members. While the receptacle 51 isillustrated as having a square cross section, it is to be understoodthat other configurations, such as triangular, etc., could be used aswell. The fingers 62 are constructed to have a cross section that issymmetrical on opposite sides of longitudinally bisecting planesextending between the ridges 59 and the longitudinal axis of the cableconnector 50. Accordingly, the inward force applied by the ring 63 tothe flattened ridge surfaces is distributed fairly uniformly on bothsides of the bisecting plane to the inner contact surface of the fingers62.

The upper end of the tubular housing 34 carries a conical skirt 65, FIG.2, so that a pair of spring latches 66 carried on the grounding cover 32can engage with the conical skirt 65 in any radial direction. The springlatches 66 include latch loops 67 designed to be engaged by standard hotline tools for latching or unlatching the various devices which carrythe standardized mating surfaces and latching elements. Suitable latchsprings 68 maintain the spring latches 66 in tight assembled relation.

The connector 50 also includes a switch connector 50b for interrupting acircuit under load. The switch connector 50b includes the samecomponents as the cable connector 50a but additionally hasarc-extinguishing components. Specifically, the switch connector 50bincludes a switch receptacle 51a defining a switch cavity 53a formed bythe fingers 62. The tension ring 63 affords inward pressure to thefingers 62 in like manner as in the cable connector 50a. The switchconnector 50b will accommodate a coupling conductor or switch member toprovide an excellent electrical connection.

To provide for load-break features, the upper connector opening carriesa liner 72 of arc-extinguishing material which co-functions with afollower 73 of arc-extinguishing material within the switch cavity 53aof the switch receptacle 51a and which is backed up by a projectionspring 74 to provide load-break effects when an associated couplingconductor is removed from the switch receptacle. The material of theliner 72 and follower 73 possesses desired arc-quench properties and maybe of synthetic polymer material carrying a suitable amount ofarc-quenching material such as molybdenum sulfide or alumina.

In operation the follower 73 moves into the opening in the liner 72 whena coupling conductor 77 of the grounding cover 32 is removed from theassociated switch cavity 53a. The cooperation of the arc-quenchingelements 72 and 73 extinguishes any arc that may be formed as thecoupling conductor 77 leaves the end of the switch connector 50 byde-ionization of the plasma. Since the arc is interrupted in the narrowspace between the follower 73 and the liner 72 and since the follower 73remains in the opening, there is no significant amount of ionized gasbetween the separated circuit elements. That is, the ionized gasesassociated with the receptacle side of the circuit remain inside andthose associated with the connector side of the circuit are dissipatedon the outside.

The connector 50 is in a receptacle chamber 80 in the relatively highpotential field associated with the cable conductor. This region wouldtherefore be subject to corona problems unless all the air spaces aroundthe receptacle are eliminated. This is accomplished according to thepresent invention by applying a conductive layer or member 81 to theinside wall of the chamber 80. If desired, the conductive layer 81 maybe a conductive paint or coating.

The inside wall of the receptacle chamber 80 includes two peripheralgrooves 82 and 83 of semi-circular cross section, one 82 at the cableentrance end which serves to reduce the voltage gradient at the end ofthe conductive layer 81 because of the enlarged radius of curvatureprovided by the conductive surface of the groove, and one 83 generallycentrally of the receptacle chamber 80 which serves to lock theconnector 50 in proper position in the chamber by means of a metallicspring ring 84. This ring 84 also serves to connect electrically theconductive layer 81 to the connector 50.

The outer surface of the hard dielectric filler 40 is also provided witha conductive layer or member, shown in the form of a conductive coating85 in the regions where it is normally in contact with the metal housing34. This is to prevent ionization of air in the small gap between theinside surface of the housing 34 and the outside surface of the filler40 which may occur due to differences in the thermal expansioncoefficients of the two materials. This problem of differing thermalcoefficients of expansions also occurs between the soft dielectricfiller 38 and the metal housings 34 and retainer 39. However, in theselocations the action of the latch springs 68 and the thrust spring 37 onthe soft elastomer keeps all of the critical interfacial surfaces invoid-free contact throughout the ranges of expected ambient temperaturesand operating conditions.

The grounding cover 32 serves to provide a positive ground to a cableterminal 30 when it is desired to work in the area of a disconnectedterminator. To this end, the coupling conductor 77 of the groundingcover is electrically connected to a metal grounding housing or cap 88which in turn is grounded to the spring latches 66 and the conical skirt65 to the grounded conducting housing 34 of the cable terminal. However,an additional ground connection is recommended to the grounding caphousing by means of a flexible ground wire connected to the terminal88b. A soft dielectric filler 90 fills the grounding cap around thecoupling conductor 77 and forms a void-free interfacial engagement withthe conical sealing surface 41 of the cable terminal. As heretoforedescribed, the latch springs 68 serve to maintain a permanent void-freeinterfacial seal between the critical interfacial surfaces in a mannersimilar to the thrust spring 37. Thus, there is provided the standardconical sealing assembly with the hard dielectric filler 40 having theconvex sealing surface 41, while the mating soft dielectric filler 90has a concave mating surface 91, which, in the illustrated embodiment,are both conical in shape.

The structure shown in FIGS. 1, 2 and 3 is particularly adapted toreceive the co-axial cable 45 which employs the plurality of wires 48arranged in symmetrical spirals over the outside surface of the cable.These wires serve as the neutral conductor of the circuit as well as agrounded protective sheath. Since these wires 48 are part of the powercircuit, they must provide a high conductivity path throughout thecircuit. For this reason, the lower cover 35 is provided with extensionmembers 92 which receive split bolt connectors 93 for holding thestrands 48 of the neutral conductor so as to make connection and at thesame time hold the cable firmly in place. The neutral wires 48 can thencontinue on to be grounded to ground or other neutral wires ashereinafter described. The extension member 92 also serves as means forrotating the cover 35 into the closed and latched position.

FIGS. 6, 7 and 8 illustrate a simple typical switch connection betweentwo cable terminals of the type heretofore described. As thereinillustrated, a pair of cable terminals 30 identical to that heretoforedescribed, are supported in spaced relation from a grounding rod 95 by asuitable mounting clamp 96. The mounting clamp 96 is precisely machinedto match the diameter of the terminal housing 34 and includes a groove97 accommodating a rib 98, FIGS. 1 and 2, which is precisely located onall of the terminal housings 34. The mounting clamps 96 are slotted withgrooves 97 so as to fit the rib 98 whereby all of the terminals 30 arerigidly held in place at the proper level with respect to the mountingclamp 96. Thus, all terminals 30 in a single mounting clamp will benormal to the plane of the bracket, at a standard distance apart and ata standard level permitting complete interchange of removablecomponents.

As best illustrated in FIG. 6, the neutral wires 48 of the cables 45 aredivided into two parts, one half going to one extension member 92 andthe other half to the other extension member 92 of a respective terminal30. This is done in order to balance the forces holding the cable inplace and also to keep all of the neutral wires tight and uniformlycovering as much of the cable sheath as is possible. A grounding clamp99 on the grounding rod 95 serves to join all neutral wires together andto connect them to ground.

The pair of cable terminals 30 in FIG. 6 are connected by a U-shapedswitch coupler 100, also illustrated in FIGS. 7 and 8, and provided witha loop 101 for engagement with a lineman's hot stick. The switch coupler100 includes a central conducting assembly made up of two switchcouplings or pins 104 serving as switch blades and braised or otherwisesecured to a crossbar 105 formed of electrically conducting materialssuch as copper. The switch couplings are silverplated and carry a switchtip 104a which is controlled in size so as to fit the switch cavity 53ain the mating cable terminal. The horizontal portion of the centralconducting member carries a cylindrical molding of conductive plastic orother suitable material 106 to enlarge the radius of the conductiveportions and reduce the potential gradient. This cylindrical molding ofconductive material 106 eliminates corona problems from air gaps in highgradient regions which could develop due to differences in thermalcoefficients of expansion between plastics and metals. With thisconstruction the field starts at the outer surface of the conductivematerial 106 which is surrounded in bonded, void-free relationship witha hard dielectric filler 107 of the same expansion coefficient as theconductive material 106 so as to remain sealed at all temperatures. Theentire assembly is enclosed within a conductive housing here illustratedas a stainless steel housing 108, formed of mating housing portions 108aand 108b, so that the filler assembly including the contact plugs 104,crossbar 105, conductive material 106, and hard dielectric filler 107may be prefabricated and then assembled within the housing. The housingportions 108a and 108b may be gripped in place together such as by theoverlaps 108c. The housing 108 is closed by end caps 109 which may bespot welded into position as shown.

The standardized conical sealing surface 41 of the cable terminal 30must be mated with a soft dielectric in order to establish the void-freeinterface under the spring forces of the standard latch system. This isaccomplished by providing conical cavities 110 around the switchcoupling 104 in the dielectric filler 107 which are larger than thestandardized conical sealing surface 41. A soft dielectric molding 111is preformed with the exact geometry of the space between the conicalactivities 110 and the conical sealing surfaces 41 to provide thestandard conical sealing surface 91. The soft dielectric fillers 110 areformed of double cones bonded to the hard dielectric filler 107 on thecoupler 100 to provide a permanent void-free interface between the hardand soft dielectrics in the coupler 100. Each of the downwardlydepending portions of the coupler housing are provided with a pair oflatch springs 66 at the ends of latch loops 67 and adapted to be loadedthrough latch springs 68 in the manner described in embodiment of FIGS.1, 2 and 3.

By the proper selection and arrangement of grounded surface elements, avariety of important distribution system functions can be performedaccording to the present invention. FIGS. 9, 10 and 11 illustrate, forexample, an assembly 120 of standard elements arranged so as to providea single fuse tap, illustrated in phantom at 114, on an undergrounddistribution loop circuit. Sectionalizing functions are provided bymeans of two switch couplers 100 of the type illustrated in FIGS. 6 to8. The necessary interconnections are established by means of a threeterminal manifold or bus 115 and three cable terminals 30. Each cableterminal 30 is identical with that of FIGS. 1, 2 and 3. In addition, themanifold 115, as illustrated, is provided with three vertical risers orcable terminals 116 each containing similar load-break features. Thus,each riser 116 is an exact replica in form and function as the upper endof the standard cable terminal. Each riser housing includes a locatingrib 117, FIG. 11, and latching cone 118 so that all removable componentswill interfit. Thus, one of the risers 116 and one of the cableterminals 30 are tied together by the mounting clamp 96 onto thegrounding clamp 95. The remaining two vertical risers 116 and cableterminals 30 are connected by a 4-place mounting clamp 122 secured to agrounding rod 123. Each of the clamping portions of the mounting clamp122 is provided with a circumferential groove 124, FIG. 10, receivingone of the locating ribs 98 and 117 to vertically position therespective terminals.

The design details of the multi-terminal manifold 115 will be moreclearly understood by reference to FIG. 11. As therein illustrated, themanifold 115 includes a central conductor 128 which may be of copper orother suitable material. Standard switch connectors 50b, identical withthe switch connectors 50b of the connector 50 illustrated in theembodiment of FIGS. 1, 2 and 3, are braised to the central conductor128. Briefly, therefore, the switch connectors 50b each include theswitch receptacle 51a provided with the switch cavity 53a for receivinga mating connector rod. As heretofore described, the switch receptacle51a is similar to the switch receptacle 51a illustrated in FIGS. 4 and 5and include the plurality of fingers 62 encircled by the tension ring63. The liner 72 of arc-quenching material leads into the switch cavity53a, and the projectable follower 73 is biased into the liner 72 by theprojection spring 74 when connecting components are not in place. It isunderstood that the load-break components including the sleeve 72,follower 73, and projecting spring 74 may be omitted where it is notdesired to provide for breaking of the circuit under load.

In like manner as with the switch coupler 100 illustrated in FIGS. 7 and8, a conductive material 130 is cast around the middle connectingcircuit components thereby enlarging the radius of the conductingportion and reducing the potential gradient. Thus, there is eliminatedthe corona problems from air gaps in high gradient regions which coulddevelop due to differences in thermal coefficients of expansion betweenthe metal parts and the dielectric fillers. With this construction, thefield starts at the outer surface of the conductive material 130.However, since the upper ends of the switch receptacle 51a in the regionof the follower 73 must be movable, a soft cover 131 of plastic or othersuitable material covers the free end of the switch receptacle 51a. Ahard dielectric filler 132 is molded over the entire conducting systemwith the outside surfaces conforming to a housing 133 of stainless steelor other suitable material and with the standard conical sealing surface41 of each riser position. The entire manifold assembly 115 may bepreformed and inserted into an upper housing portion 133a with a lowerhousing portion 133b slipped into position and with end caps 134 spotwelded into place. As in previous components, the outside surface of thehard dielectric filler 132 is covered with a conductive layer 135 excepton the conical sealing surfaces.

The risers 116 may be provided in any number; however, most circuitrequirements can be met with three or four terminal manifolds. It shouldbe noted that the risers are arranged in line and spaced the standarddistance apart. Also, the vertical sleeve portions of the housing 133are fully standardized to fit brackets and to mate with removablecomponents. Thus, two four terminal manifolds can be combined to providesectionalized switches and four fused taps in a single control center.

Surge production is frequently desired at the open end of a loop circuitor other suitable locations when it is to remain in this condition for along period of time. FIG. 12 illustrates in partial cross section asurge arrestor 140 which may be connected to any of the standardterminals in a cluster or control center. The surge arrestor 140includes a grounding housing 141 of stainless steel or other suitablematerial and includes a lower portion 141a which is standardized withthe conical sealing surface 91 to the fit cable terminals andmultiterminal manifolds of the grounded surface distribution system.According to the present invention, the functional parts of the surgearrestor 140 include a system of quench gaps 142 in series with valveblocks 143 of suitable material such as silicon carbide. These elementsare arranged in a dielectric tube 144 under compression of a compressionspring 145. The housing includes a top cover 146 locked to the remainderof the housing through side pins in like manner as cover 35 in theembodiment of FIGS. 1, 2 and 3. The space between the dielectric tube144 and the metal housing 141 is filled with a soft dielectric filler147 which is maintained in void-free interfacial contact by means of theinner thrust spring 37 acting between the end cover 146 and the retainer39. A connector pin 148 extends from the lower end of the surge arrestor140 for mating within the switch cavity 53a of a collaborating member. Acone of soft dielectric material 149 is placed around the upper end ofthe contact plug 148 in order to control the gradient in this region. Itis understood that the connecting components of the lower housing 141aare identical to those heretofore described, including the springlatches 66, the latch loops 67, and the latch springs 68 which serve thedual function of biasing the spring latches 66 and applying a positivepressure to the dielectric filler 147.

To provide for fusing of the grounded surface distribution system, oneof the interchangeable elements may consist of a current limiting fuse,such as the current limiting fuse 152, illustrated in FIG. 14. Astherein illustrated, the current limiting fuse 152 is housed within anassembly similar to the switch coupler 100 more fully described in thediscussion of FIGS. 7 and 8. More specifically, there is provided thefuse unit 153 enclosed within a metal housing 154, similar to housing108 heretofore described, and cast in the center of a hard dielectricfiller 155. A pair of conically shaped soft dielectric fillers 156 areprovided having the standard conical sealing surfaces 91 for engagingthe conical sealing surface 41 of cable terminals or manifolds, and thefuse 152 is provided with the standardized latches to interfit with theother components.

Referring now to the fuse unit 153, the operation thereof is known anddepends upon the melting and vaporization of a silver fuse wire 157 andthe subsequent deposition of the silver over the surfaces of sand grains158 which surround it. This takes place so rapidly under high faultconditions that the current is cut off before it reaches the full valueof the available fault current. The silver metal becomes so diffused inthe sand grain matrix that it no longer carries significant current. Insuch fuses it is necessary to maintain sufficient distance between theturns of the silver wire to prevent hot ionized gas from shorting outturns. In the illustrated design, in order to minimize the length of thefuse for a given rating, a wide flange surrounding the spiral core 159is used to separate the turns of the silver fuse wire 157. As previouslymentioned, this space around the wire between the spiral flanges isfilled with refractory granules such as alumina or silica. The granularmatrix may be bonded with a minimum of refractory cement in order topermit the assembly of the parts within an insulating tube 160. The tube160 may be of organic or inorganic material, but preferably it is ofhigh strength and refractory at least in its lining in order to minimizeinternal pressures which may develop during operation. This fuse has nooutlet for gaseous discharge since its entire envelope must be capableof withstanding system voltages within the grounded housing. Therespective ends of the silver fuse wire 157 is soldered to the center ofopposed cylindrical ferrules 161 fitted over the ends of the surroundingspirals 159 and insulating tube 160. Thus, the silver fuse wire 157 maybe of maximum length. A pair of contact rods or plugs 162 extendconcentrically through the soft dielectric filler for engagement withina plug receiving cavity 153 of a conductor assembly 50.

In order to control the potential gradient around the turns of the fusewire in the sand and thus prevent corona in this region, a conductivefilm is applied to the outer surface of the fuse tube 160. A terminal toterminal resistance in the range of 50 to 150 megohms providessatisfactory operation of the fuse.

In the above fuse design, the active fuse wire 157 is not removable inthe field from the matrix of the hard dielectric filler 155. When blown,the fuse 152 will have some salvage value for factory rebuilding, butcannot be rebuilt in the field. FIGS. 15 and 16 illustrate a currentlimiting fuse 165 which, although somewhat more expensive initially thanthe fuse 152, may have the active element replaced by the user in thefield, and the fuse unit 165 could go back into service immediately.

The principle of operation of the fuse 165 is similar to that of fuse152 and includes the silver fuse wire 157 between the flanges of thespiral core 159 filled with suitable refractory granulars or sand grains158. This active fuse element is housed within removable fuse cartridge166 which can be removed from a metal housing 167 for replacement byreleasing one or both of a pair of opposed end thrust spring covers 168and unscrewing a pair of contact rods or plugs 169 from plug blocks 170.In the fuse 165, the entire space between the housing 167 and the fusetube 166 is filled with soft dielectric filler 171 and is maintained invoid-free contact by end thrust springs 172 interposed between thespring covers 168 and respective retainer cups 173. A bayonnetconnection joins the spring covers 168 with the housing 167 in a mannersimilar to that illustrated in the embodiment of FIGS. 1, 2 and 3. Theconical sealing surface 91 is maintained on the soft dielectric toengage the conical sealing surface 41 of a cable terminal, manifoldriser or the like. The conical sealing surfaces are maintained invoid-free contact by the latching system heretofore described includingthe spring latches 66, latch loops 67, and latch springs.

The grounded surface distribution system according to the presentinvention is versatile and permits numerous combinations of standardelements to provide a variety of circuit control centers. There isillustrated in FIGS. 17 to 20 a two-level tap arrangement for a controlcenter which permits some reduction in space and in the number ofcomponents required. However, these components are not fullyinterchangeable with the previously described standard components. Astherein illustrated, for example, there is shown a switching or controlcenter wherein a tap 178 is taken from a main line 179, 180. Each of thelines and the tap, 178, 179 and 180 includes a respective cable 181,182, 183 terminating in the cable terminals 30 similar to that describedin the embodiment in FIGS. 1, 2 and 3. Each of the cable terminals 30 issupported by a three way mounting clamp 184 from a grounding rod 185.Each of the cables 181, 182 and 183 is of the grounded surface typehaving the plurality of strands 48 of grounding wire which are firstsecured to the extension members 92 on the respective cable terminals30, and are run through a ground clamp grounded to the grounding rod 185in the manner previously described. The cable terminals 30 associatedwith the line 179, 180 is supported at the same vertical level; however,to provide the multi-level tap, the tap assembly 178 is supported at ahigher elevation. To this end the housing of the cable terminal 30 maybe provided with suitable locating means such as a detent or the like.

To provide suitable control functions, there may be provided a line fuse190 of the current limiting type and interconnecting the line assemblies179 and 180 in a conventional manner. However, additionally the linefuse 190 is provided with an upwardly extending standard conical sealingportion 191 having the standard conical sealing surface 41 and defininga tap from the line 179, 180.

To provide for connection of the tap 178, there may be provided a tapfuse 192, similar to that heretofore described, but having one of itsstandard sealing portions longer than the other joining between thecable terminal 30 of the tap 178 and the sealing portion 191 of the linefuse 190. Thus, there is provided a switching center wherein either line179-180 of a loop may be isolated, or alternatively the tap 178 may beisolated. Isolation of one line 179 is illustrated in FIGS. 19 and 20.In this embodiment the line fuse 190 has been removed, and the tap fuse192 has now been connected between the tap 178 and the line 180. Inaddition, the grounding cover 32 is shown on the isolated line 179. Anisolating cover also may, if desired, be applied to this component.

The tap can also be connected directly to the terminal of a component byusing an L-shaped coupler 200 illustrated in FIG. 21. As thereinillustrated, the L-coupler 200 is connected directly to a terminal 201of an electrical apparatus fragmentarily illustrated at 202. Theterminal 201 includes the connector assembly with the switch connector50b cast within a hard dielectric 203, and similar to the switchconnector 50b of the connector 50 more fully described in the embodimentof FIGS. 1 through 3. However, briefly, the switch connector 53aincludes the socket member 51a provided with a plurality of fingers 62biased together by the tension ring 63. The follower 73 will projectthrough the liner 72 under the force of the compression spring 74 toprovide the arc-extinguishing feature of the terminal. The terminal 201,of course, is provided with the standard conical sealing surface 41 andthe conical skirt 65 to provide latching thereto.

The L-coupler 200 includes a conducting housing 204 enclosing a cableconnector 50a, similar to that described in the embodiment of FIGS. 1, 2and 3. Briefly, the cable connector 50a includes the receptacle 51having a plurality of fingers 62 biased together by the tension ring 63and defining the pin cavity 53. The pin 52 is secured to the end of thetap cable 45 and is received within the pin cavity 53 to provide theconnection between the cable 45 and the cable connector 50a. Thecoupling connector 77 extends from the cable connector 50a at rightangles thereto. The entire connector cable and cable 45 is encasedwithin a soft dielectric 204 held under compression to provide void-freeinterfacial engagement by means of the thrust spring 37 interposedbetween the cover 35 and the cup retainer 39. The coupling conductor 77is receivable in the pin cavity 53 of the cable connector 50a in theterminal 201. The soft dielectric is provided with the standard conicalsealing surface 91 engageable in void-free relationship with the conicalsealing surface 41 by means of the standard latches and springs.

Although the L-coupler 200 could be used in a switch center or clusterof cable terminals 30, it has particular usefulness as a connection tosuch electrical apparatus as transformers and circuit breakers.Moreover, it is noted that only in the case of the L-coupler 200, theline cable 45 remains with the removable switching component.

It is, of course, necessary to provide for cable splicing or joining andto this end there is provided a cable splice 210 illustrated in FIGS. 22to 24. The two ends of the cable splice 210 are identical, andaccordingly, only one is illustrated and described in detail as shown inbroken away cross section. The splice includes a conducting housing 211of stainless steel or other suitable material and including at both endsthe covers 35, each of which engages the two side pins 36 in a spiralbayonnet action permitting the inner thrust spring 37 to be compressedin the latched position as shown so as to exert an axial thrust on asoft dielectric filler 212 by exertion of load against the cup retainer39. The soft dielectric filler 212 is designed to receive the ends 213,214 of a power cable 213, 214 similar to the cable 45 heretoforedescribed. The end thrust springs 39 permit a reasonable range indiameter variation and still maintain a very permanent void-freeinterfacial seal between the insulation 213 and the soft dielectricfiller 212.

Encased within the soft dielectric filler 212 is a coupling 215including two opposed cable connectors 50a, each identical to the cableconnectors 50a illustrated in FIGS. 1, 2 and 3. Briefly, each cableconnector 50a includes a receptacle 51 and a pin 52, which pin 52 issecured to the conductor in the cables 213 and 214, respectively. Thereceptacle 51 defines a pin cavity 53 formed by a plurality of fingers62 and held with an inwardly bias by the tension ring 63. The operativecomponents of the coupling 215 are housing within a conductive cylinder216 which serves the same function as the conductive layer 81 in theembodiment of FIGS. 1, 2 and 3, and which further serves to isolate themovable portions of the coupling assembly 215 from the soft dielectricfiller 212. It will be recognized that the operative components for thecable connector 50a are identical to those illustrated in FIGS. 4 and 5.

To provide the continuous grounded surface of the system, the cables 213and 214 are each covered with the grounding strands 48 of wire and whichare secured to the extension members 92 of the respective covers 35 bythe split bolt connectors 93 thus maintaining a continuation of thegrounding conditions.

FIGS. 25 and 26 illustrate an embodiment of a circuit control center orswitching center arranged similar to that illustrated in FIGS. 17through 19, but employing a modified T-tap terminal for the terminals ofthe loop cables. As therein illustrated, there is provided a T-tapterminal 220 for terminating ends of the loop cables 221 and 222,respectively. The T-tap terminal 220 includes a pair of cable connectors(not shown), each similar to cable connector 50a described in theembodiment of FIGS. 1 to 3, for receiving pins connected to the end ofthe associated cable. The assembly is encased in the soft dielectricfiller and held under compression by the described thrust spring actingbetween the retainer and the cover. A central bus interconnects thecable connectors associated with the respective cables 221 and 222within a grounded housing 223. Moreover, a central tap or riser 224extends from the T-tap terminal 220 and includes a switch connector suchas that illustrated as 50b in FIGS. 1 through 3. The riser 224terminates in a standard conical sealing surface so as to join with theswitch coupler 100 heretofore described.

A tap line 225 is provided with a standard cable terminal 30 so that theswitch coupler 100 joins in the manner heretofore described between theriser 224 and the terminal 30. The terminal 30 and the T-tap terminal220 are held in the proper space and vertical relationship by a mountingclamp 226 secured to a grounding rod 227.

Although the T-tap terminal 220 is not fully interchangeable with othercomponents of the system, its simplicity of construction and its singleunit assembly make it desirable in some installations.

FIG. 27 illustrates a typical switching center or control center whereinthe components are positioned within a well casing 230 below the surfaceof the earth 231. As therein illustrated, there is provided a pluralityof cable terminals 30 and a plurality of multitap manifolds 115, each ofthe terminals 30 and manifolds 115 terminating in the standardizedconical sealing surfaces. Suitable functional components, such as theillustrated switch couplers 100, connect the manifolds and cableterminals in the desired manner to provide the loop, sectionalizing orother desired function. The switch couplers 100 may be removed from theswitching center by a standard hot line tool hooked through the loop 101of the responsive component. Switching couplers 100 removed from theswitching center may be set aside, such as illustrated in FIG. 27, toprovide a visual isolation of the respective lines. It is understoodthat a grounding cap, surge arrester, or other suitable component may beplaced over the terminals or manifold risers after the switch couplerhas been removed therefrom.

From the above description, it is seen that there is provided animproved grounded-surface distribution system wherein the entireelectrical structure is enclosed in metal housings thick enough toprovide mechanical support and to carry fault current if it occurs. Theentire high potential conductor system has been placed inside of thesegrounded housings with adequate coupling and transition means forcarrying out switching and sealing functions. A void-free elastomer orsoft dielectric surrounds the high voltage elements with compressionsprings at appropriate locations to maintain all critical interfacesvoid-free and under pressure at all ambient variations expected in thefield. Each circuit is maintained separately in its own grounded sheathwith interfitting components available to set up various functions suchas switching or load-break disconnect. In this simple case the two cableterminals are clamped into a rigid two-way bracket mounted on a groundrod. The switching feature is present in both cable terminalsindependent of each other. The switch blade is a grounded surfaceinverted "U" which can be removed with a hot stick from above. Theoperator moves only the coupling piece. The cables or terminals are notmoved or disturbed in operation. The hot circuits are never exposedsince the followers fill the connector openings when the switch isopened. The open circuits are visually separated and metallic groundsare between them. Insulating or grounding caps may be securely latchedover the elements of the open switch. Thus, the switch may be open withseparate caps or closed with the "U" coupling and completely safewithout hazard to operating personnel working in close proximity tothem. An important feature of this system resides in the double loadbreak which is always present since each cable terminal contains anarc-quenching system which separates both sides of the high voltagecircuit simultaneously from the removable coupler element. This insuresmore effective load break function and greater safety to the operatorand requires no movement of the energized cables except in the singleembodiment of the L-coupler illustrated in FIG. 21.

Although the present invention has been described by reference toseveral embodiments thereof, it will be apparent that numerous othermodifications and embodiments will be devised by those skilled in theart which will fall within the true spirit and scope of the presentinvention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A cable terminal for a high potential groundedsheath cable for underground distribution systems comprising:acylindrical conductive grounding housing open at one end; a harddielectric filler secured in said housing and having a convex sealingsurface projecting in the direction of said open end; a readilyremovable conductive grounding cover for said open end conductivelyengaging said housing; means for grounding said cover to the groundedsheath of a cable; a soft dielectric filler in said cover having aconcave sealing surface making void-free interfacial engagement withsaid convex surface; and compression means positioned between said coverand said soft dielectric filler to maintain said soft dielectric fillerunder pressure.
 2. A cable terminal for a high potential grounded sheathcable for underground distribution systems comprising:a cylindricalconductive grounding housing open at one end defining an electrical tap,said housing including a conical skirt; a hard dielectric filler securedin said housing and having a convex sealing surface projecting in thedirection of said open end; a conductive grounding cover for said openend conductively engaging said housing; means for grounding said coverto the grounded sheath of a cable; a soft dielectric filler in saidcover having a concave sealing surface making void-free interfacialengagement with said convex surface; and a plurality of spring biasedlatch members provided on said cover engageable over said skirt in anyradial direction.
 3. A cable terminal as set forth in claim 2 whereinsaid spring biased latch members act on said soft dielectric filler toprovide a compressive force thereon.
 4. A grounded surface control unitfor controlling a plurality of circuits and comprising:a plurality ofparallel positioned cable terminals for high potential grounded sheathcables for underground distribution systems, each of said cableterminals including:a cylindrical conductive grounding housing open atone end, a hard dielectric filler secured in said housing and having aconvex sealing surface extending in the direction of said open end, saidhard dielectric filler having a longitudinally elongated central cavityopening toward said open end, and connector components in said centralfor releasably receiving an electrical coupling pin; some of saidplurality of cable terminals including means for attachment to adifferent high potential grounded sheathed cable; a grounding member;and electrically conducting grounding bracket means supporting saidcable terminals from said grounding member at fixed distances to providefor interchangeability with removable interfitting electrical connectingunits to provide flexibility of the control unit.
 5. A grounded surfacecontrol unit for controlling a plurality of circuits and comprising:aplurality of parallel positioned cable terminals for high potentialgrounded sheath cables for underground distribution systems, each ofsaid cable terminals including:a cylindrical conductive groundinghousing open at one end to define an electrical tap, a hard dielectricfiller secured in said housing and having a convex sealing surfaceextending in the direction of said open end, said hard dielectric fillerhaving a longitudinally elongated central cavity opening toward saidopen end, and connector components in said central cavity for releasablyreceiving an electrical connector pin; a ground of said plurality ofelectrical taps being interconnected to form a multitap manifold andincluding:a common lower housing element connecting said group ofelectrical taps, said housing being conductive and electrically engagingthe cylindrical conductive grounding housing of each tap of said group,a dielectric within said lower housing, and electrical conducting meansin said lower housing interconnecting the connector components in saidgroup.
 6. A grounded surface control unit as set forth in claim 5 andincluding:a grounding member; and electrically conducting groundingbracket means supporting said cable terminal from said grounding memberwith sets of electrical taps maintained at fixed distances to providefor interconnection between taps of said group and others of said tapsand between said others of said taps with removable interfittingelectrical connecting units to provide for flexibility of the controlunit.
 7. An electrical connector for a high potential grounded sheathcable for underground distribution systems comprising:a first insulatingmember having a projecting frustoconical sealing surface and a pincavity defined therein, a first electrically conductive contact memberin said cavity, a second insulating member having a connection inletwith an inner sealing frusto-conical surface conforming to thefirst-mentioned sealing surface to produce a seal upon engagement ofsaid surfaces. a second electrically conductive contact member in saidinlet for engagement with the first-mentioned conductive contact memberon insertion of said second contact member into said pin cavity. ashield of low electrical resistance stainless steel covering at least aportion of the outer surface of said second insulating member, saidshield being formed of a pair of mating portions welded together, andmeans for electrically connecting said shield to the grounded sheath ofa high potential grounded sheath cable.